Plain-language reference
Clear definitions for the measurements, components, ratings, and design terms that come up in a thoughtful HVAC conversation.
Understand the system
These definitions provide context, not a diagnosis. The way a term applies to a property still depends on the equipment, building, measurements, and scope.
A rate describing how many times the air volume of a space is replaced in one hour.
Why it matters: ACH can help describe ventilation or air-cleaning performance, but the correct target depends on the space, system, and purpose of the calculation.
The indoor cabinet that moves conditioned air and may contain a blower, evaporator coil, filter, and electric heat components.
Why it matters: Its blower, coil condition, filter fit, controls, and access all affect comfort and serviceability.
The volume of air moving through equipment, ducts, and registers, commonly discussed in cubic feet per minute (CFM).
Why it matters: Too little or poorly distributed airflow can affect comfort, noise, equipment operation, and temperature split.
The rotating fan assembly that moves air through the indoor equipment and duct system.
Why it matters: Buildup, damage, motor performance, and system resistance can change delivered airflow.
British thermal unit, a unit used to describe heating or cooling energy.
Why it matters: Equipment capacity is often expressed in BTU per hour, but selecting capacity requires load information rather than square footage alone.
Cubic feet per minute, a measure of air volume moving through a point in the system.
Why it matters: Measured CFM helps evaluate whether rooms and equipment are receiving the airflow the design intends.
The process of checking setup, operation, controls, airflow, drainage, and other project requirements after installation.
Why it matters: A system is not complete simply because it turns on; verification connects the installed work to intended operation.
The outdoor heat-transfer section of a typical split air-conditioning or heat-pump system.
Why it matters: Coil condition, airflow, electrical components, clearances, and coastal exposure can affect operation and longevity.
Air escaping from or entering the duct system through gaps, failed connections, or damaged materials.
Why it matters: Leakage can reduce delivered comfort and move air through unintended spaces, but testing is needed to quantify it.
The indoor heat-exchange coil used for cooling and, in a heat pump, part of the reversible refrigeration cycle.
Why it matters: Airflow, cleanliness, drainage, and refrigeration operation around the coil influence capacity and system behavior.
Equipment that moves heat using a refrigeration cycle and can provide both cooling and heating.
Why it matters: Application, controls, auxiliary heat, electrical capacity, ductwork, and climate performance should be considered together.
Indoor air quality, a broad description of conditions such as particles, ventilation, moisture, contaminants, filtration, and occupant concerns.
Why it matters: IAQ is not a single product or medical diagnosis; useful evaluation starts by defining the concern and measuring what can be measured responsibly.
An engineering calculation used to estimate how much heating and cooling a building or zone requires under defined design conditions.
Why it matters: It supports equipment selection more reliably than replacing equipment solely by the size of the old unit.
An ACCA residential heating and cooling load-calculation procedure.
Why it matters: Breezy includes Manual J with every full residential system installation; that inclusion does not apply to commercial projects.
Minimum Efficiency Reporting Value, a scale used to describe how an air filter performs across defined particle-size ranges.
Why it matters: A higher rating is not automatically better for every system because filter size, surface area, bypass, and pressure drop also matter.
A split heating and cooling system, often ductless, with one or more indoor units connected to an outdoor unit.
Why it matters: Sizing, placement, drainage, line routing, controls, cleaning, and service access affect the result.
Heating and cooling equipment with major components housed in one outdoor cabinet, often connected to ducts.
Why it matters: The package still depends on controls, power, drainage, duct connections, airflow, and site access.
The reduction in air pressure as air moves through equipment, filters, coils, fittings, and ductwork.
Why it matters: Each component adds resistance; the combined pressure relationship helps explain airflow limitations.
The working fluid that changes pressure and state as it moves heat through an air-conditioning or heat-pump system.
Why it matters: Refrigerant work requires qualified service practices; low cooling performance is not proof of a refrigerant leak or a need to add charge.
Air drawn from the building back toward the HVAC equipment through return grilles and duct paths.
Why it matters: Restricted or poorly located return paths can affect pressure, airflow, noise, and room-to-room comfort.
A seasonal cooling-efficiency metric used for current residential equipment ratings under updated test procedures.
Why it matters: It supports equipment comparison but does not by itself predict a specific home's bill or correct poor duct delivery.
Resistance to airflow measured in the HVAC system, commonly expressed in inches of water column.
Why it matters: Static-pressure readings help evaluate the combined resistance of returns, filters, coils, supplies, and duct components.
The temperature difference between return air entering the equipment and supply air leaving it under defined conditions.
Why it matters: It is one diagnostic input, not a complete diagnosis; airflow, indoor conditions, equipment stage, and measurement location matter.
Variable refrigerant flow, also marketed by some manufacturers as variable refrigerant volume, uses inverter-driven refrigerant systems to serve multiple zones.
Why it matters: Design requires careful load, piping, controls, ventilation, access, and service planning; VRV is a brand term used by Daikin.
A control and air-distribution strategy that serves areas independently using compatible equipment, controls, and often motorized dampers.
Why it matters: Zoning is not simply closing registers; bypass, minimum airflow, control logic, duct design, and equipment operation must be coordinated.
The next measured step
Tell us what the property is doing. Breezy will help choose the right starting point.
